The present invention relates to the art of electric arc welding and more particularly to an apparatus and method for short circuiting arc welding.
Short circuiting arc type electric arc welding has been employed for many years; however, this type of welding, with its many advantages, has had substantial disadvantages. For instance, it has been limited to a relatively low rate of deposition. In addition, short circuiting arc welding has been capable of employing only a relatively low energy level and has produced non-uniform weld beads requiring post welding operations. In addition, the shielding gas used with short circuiting arc welding often required at least a portion of an expensive inert gas, such as Argon so that an electric pinch action can be employed for transferring molten metal from the driven welding wire to the molten metal pool during the short circuit stage or condition of the short circuiting arc welding process.
As the welding wire is fed toward the molten pool during the short circuiting arc welding process, the process alternates between a condition with the wire spaced from the weld pool with a gap separated by a plasma or arc, known as the arcing condition, and a condition with the welding wire touching the weld pool for the purpose of transferring molten metal from the electrode into the weld pool, known as the short circuit condition. In the past, these two conditions were natural phenomena created by using a constant voltage power supply and by driving or feeding the welding electrode toward the weld pool at a preselected feed rate. During the arcing condition, a ball of melted metal would be formed on the end of the advancing welding wire. When the ball grew to a sufficient size it would contact the weld pool causing a short circuit and initiating the short circuit condition of the welding process. Output characteristics of the power supply controlled the current flow during the arcing and short circuit conditions. Consequently, the size of the melted metal ball on the end of the advancing electrode or wire was determined by mechanical, electromagnetic and arc parameters which varied during successive cycles of the process. The size of the ball on the end of the wire was inconsistent and the resultant weld bead on the workpiece was not uniform. For that reason, the energy employed for short circuiting arc welding was relatively low so that a low total melting rate was obtained producing a low deposition rate during the total welding process.
Even with the various disadvantages and difficulties experienced in short circuiting arc welding, the industry has been anxious to develop this system for the purpose of high production welding; however, these efforts have been primarily thwarted by an preeminent disadvantage of short circuiting arc welding, i.e. high spatter associated with high energy arc alternating between short circuit conditions. Operators were aware of the spatter problem more than operational limitations on the process. Bead appearance was unsatisfactory and the welding tube became clogged by spattered metal. It is not surprising that these apparent limitations took precedent whereby the efforts in recent years to develop improved short circuiting arc welding apparatus and methods have been devoted primarily to the concept of reducing spatter. The reduction of spatter decreases the most obvious disadvantage of short circuiting arc electric welding as experienced by the operator; however, it did not allow higher deposition rates, large welding wires to produce a desired weld bead having a uniform appearance at high speed or really address more basic, yet less apparent limitations in prior attempts to improve short circuiting arc welding.